This invention relates in general to foam compositions, and more specifically to foams that are elastic above the glass transition temperature (Tg) and rigid at room temperature, and that possess hibernated elastic memory in the rigid state.
U.S. Pat. No. 4,725,627 to Arnason et al. discloses a squeezable toy which is said to possess dimensional memory. The toy is made from an elastic material that will change dimension under force, and when the force is removed it will return to its original shape. There is no suggestion of a foam that is elastic above the Tg and rigid at room temperature, and that possesses hibernated elastic memory in the rigid state.
U.S. Pat. No. 5,032,622 to Herrington et al. discloses a densifiable and re-expandable polyurethane foam. The Tg of the foam is very broad, starting at a temperature well below room temperature. As a result, the foam retains some elastomeric character at room temperaturexe2x80x94it is not rigid at room temperature. The foam can be flexed and compressed at room temperature. As an illustration, the patent describes crushing the foam at room temperature to mechanically open the cells of the foam. If the foam was rigid at room temperature, the crushing would break and destroy the foam.
U.S. Pat. No. 5,418,261 to Helsemans et al. discloses polyurethane foams having shape memory. The foams are prepared with polyoxyalkylene polyols containing oxyethylene residues. The polyols have an average oxyethylene content of at least 86% by weight. Foams prepared with oxyethylene based polyols have various disadvantages, such as hydrophilicity and other shortcomings, that limit the applications of the foams.
xe2x80x9cCold hibernated elastic memory (CHEM) self-deployable structuresxe2x80x9d, Sokolowski et al., SPIE ""99 International Symposium on Smart Structures and Materials, Mar. 1-5, 1999, describes shape memory polymeric foams and structures made with the foams. There is no disclosure of the chemical structure of the foams.
The invention relates to a polymeric foam, preferably a polyurethane foam, having a glass transition temperature, Tg, which is at or above room temperature (21xc2x0 C.). The foam is rigid at room temperature and elastic above the Tg. The foam has shape memory such that when it is deformed at a temperature above the Tg and the temperature is then lowered to room temperature or below, the foam retains its deformed shape, and when the temperature is then raised above the Tg the foam returns substantially to its original shape. In other words, the foam possesses hibernated elastic memory in the rigid state. The foam is also hydrophobic, which allows it to be used in many applications where hydrophilic foams are unsuitable.